Oil bearing surfaces such as typically found in cylinders or cylinder liners of internal combustion engines, or piston-cylinder assemblies, commonly called linear actuators, have special material surfaces. These surfaces have a special topography and are usually formed first by a rough hone and then a finish hone. both rough and finish hones are "stones" mounted in a honing machine head which rotates and axially translates the stones within the cylindrical bore of the surface. Both rough and finish hones are usually mounted in the same honing machine head and the operations take place sequentially at the same location. Also used in the rough and finish operations are steel holders with abrasive minerals plated thereon. In either case the tool is rigid and presents in the operation an unyielding abrasive-work interface.
The resultant surface has folded over peaks, folded over metal and debris in the bottom of the cross hatching oil grooves. This is true even though the surface is constantly flushed with lubricant or coolant during the honing operations.
In operation, the rough honing tools which contain a coarse adbrasive grit are pressed against the cylinder walls to perform the work required. After a predetermined time cycle the rough honing tools are retracted into the honing head and the finish honing tools, containing a very fine abrasive grit, are pressed against the cylinder walls during the final finishing operation.
The rough hone forms in the surface a pattern of ridges and grooves, almost like a cross hatch pattern. These grooves or striations are the oil retention pattern against which the piston or piston rings ride. Unfortunately when the rough hone operation is completed the surface greatly enlarged shows deep peaks and valleys or other sharp projections which can break off, and which would contribute to piston or ring wear, and all of the detrimental performance, life and environmental problems associated therewith. For example, ring or piston wear is the cause of "blow by" which can create all kinds of emission problems in an internal combustion engine. The purpose of the finish hone is to smooth over the peaks and valleys.
It has been discovered that rigid finish hones, while somewhat improving the topography of the surface, can in many instances actually contaminate the surface by driving or embedding dislodged hard abrasive particles into the surface. This has been determined by photomicrographs and by tests of engines and engine oil after break in. The particle is usually driven into the slope or crown of a ridge which is the seal bearing surface. Thus, instead of the surface being improved, it has been made worse. A projecting hard abrasive particle will score a piston ring or seal causing premature failure, blow by, and poor engine efficiency, for example, and most of the other problems honing is supposed to address.
During recent years, to correct these problems and to improve upon the final finishing results, a second honing head was added to a few high production automotive engine block lines directly after the rough and finishing honing operation. The honing tools used were superabrasives plated on very fine wire filaments, lightly filled, and fine abrasive nylon brushes. Results of this added operation have been questionable based upon quality improvements and economic justification.
A second head brush hone using very fine spaced bristles may be seen in European Patent Publication 0 247 572. A post hone brushing machine is also seen in U.S. Pat. No. 5,042,202. In U.S. Pat. No. 4,980,996 there is illustrated a machine using tufted spaced bristles in combination with a high pressure spray or jet to remove metal nap after honing.
Also recently used in post honing second station operations are honing tools of the type shown in the copending application of Scheider and Warner, Ser. No. 07/508,060, entitled "Abrasive Filament Honing Tool And Method of Making And Using The Same", filed Dec. 14, 1989 now U.S. Pat. No. 5,216,847. The tool of this copending application comprises tightly packed nylon-abrasive filaments which form a dense and compact slightly yieldable face. Such tool has been performing adequately in post honing, second station operations to improve honed surfaces.
It would be advantageous to combine the post honing second station operation using the abrasive filament honing tool, with the rough hone operation, thus eliminating the conventional finish hone operation, as well as the second station operation. This would eliminate the requirement for expensive finish hones, and would also eliminate any contamination caused by such hones. It would also significantly shorten and simplify the entire honing operation. The advantage of such a combination and the elimination of the finish hone step can only be realized if proper or improved surface topography is obtained. Applicants have discovered that it is.